Autographa californica nuclear polyhedrosis virus (AcNPV) has been adopted as a model system by baculovirologists throughout the world. A major motivation to study baculoviruses is the current use of these viruses as biological insecticides. In order to more thoroughly understand the nature of baculoviruses and the basic mechanism of infection, genetic and biochemical studies have been undertaken which are primarily directed at determining the type and organization of viral genes, the mechanism of expression of these genes and the function of the gene products. Genetic characterization of AcNPV in our laboratory has primarily entailed the isolation of temperature sensitive (ts) mutants, the construction of a physical map of AcNPV and the correlation of genetic mutations with specific regions of the physical map. Marker rescue methods involving transfection of the insect cell lines with mutant viral DNA and wild type restriction fragments were developed specifically for correlating ts mutations and the AcNPV physical map. A series of mutants with poor plaquing at the restrictive temperature (i.e., mutants with some defect in extracellular nonoccluded virus formation) have been successfully mapped. Work is continuing to isolate and map a larger number of mutations. In terms of characterization of mutational defects, it is necessary to better define, biochemically, the nature of the infection process. To this end, a screen of virus-induced enzymes has been undertaken. A new DNA polymerase is induced upon AcNPV infection and will be further characterized. Other enzymes will also be tested for induction and/or presence in the virus particles. As a preliminary step to studying the mechanism of gene expression at the level of RNA transcription, the cloning of AcNPV DNA restriction fragments has been undertaken. Upon completion, transcriptional studies will be initiated.